Creating a truck exhaust mesh
For creating a real mesh you can use the array and boolean modifiers as follows :


create a cylinder 'C1' and put in the right position 
add an empty 'E1' rotate it 36° 
add an array modifier to C1 and use E1 as offset object, with a count of 5
add a second empty 'E2' and rotate it 18°
add array modifier to 'C1' and use 'E2' as offset object,with a count of 10 or more
create a cylinder 'C2' and put in the right size and pose 
remove the top and bottom faces of 'C2'
add a boolean modifier with target set to 'C1' and type to 'Difference'
parent 'C2','E1' and 'E2' to 'C1' and hide them (so you don't need to apply the modifier until you are satisfied with the results)




Note : i have add Bevel modifier to 'C1' and subsurf and solidify to 
'C2'  to get the previous result 



To avoid having a dense mesh and dealing with the boolean modifier you can use a texture and transparent material to achieve the same results :


use the following node setup for the material (you can replace the defuse with more complex shaders )
use Follow active quad to unwrap the cylinder and map it correctly on the texture 
if the texture has an alpha channel use it instead of the RGB_BW converter in the material nodes




The result render :